This invention relates to an accumulator.
Accumulators provide a temporary reserve of fluid under pressure. Typically the pressure source is a trapped volume of gas contained within the accumulator housing and separated from the fluid. The pressurized fluid can be used in hydraulic systems to supplement the output from the pump or to act as a fixed source of fluid for when the hydraulic pump is not energized so that, for example, the brakes on an aircraft will properly operate even when the engines are not running.
In one prior art accumulator, a separator (e.g., the combination of a piston in a chamber connected to the chamber by a bellows type seal) separates the compressed gas from the non-compressible hydraulic oil. When the hydraulic pump is operating, the hydraulic oil pressure drives the piston to compress the gas. When the hydraulic system pressure drops below the gas pressure, however, the piston moves under the action of the gas pressure displacing stored hydraulic fluid into the system as required. When the hydraulic system is shut down or hydraulic fluid leaks out, the piston goes to a full stroke stopped position and the gas pressure alone can then adversely act on the bellows and the piston. See U.S. Pat. No. 5,638,868 incorporated herein by this reference.
To alleviate the stress caused by this situation, the ""868 patent proposes the use of a valve mechanism incorporating an arrow-shaped poppett with a contact pin therein connected to a compressible inner spring which captures enough fluid in the accumulator to prevent the piston from bottoming out. This design is, however, somewhat limited by, inter alia, frictional forces between the poppett and the housing. To close the valve, these forces must be overcome by the spring force and contamination or surface deterioration will add to the force and, in limiting circumstances, result in hangup of the poppett. Also, when the accumulator is in operation and the valve is open, a high demand of hydraulic fluid will tend to cause the valve to close restricting or limiting the accumulator performance capability.
It is therefore an object of this invention to provide an accumulator wherein the force driving the sealing mechanism is not dependent on a spring.
It is a further object of this invention to provide such an accumulator which allows for the use of a single seal, and which provides a large closing force.
It is a further object of this invention to provide such an accumulator in which, during operation, the sealing system is remote from the fluid port and has no influence on the accumulator performance even under conditions of high demand.
It is a further object of this invention to provide such an accumulator which has no sliding surfaces and hence no frictional forces.
It is a further object of this invention to provide such an accumulator which can incorporate a replaceable sealing seat.
It is a further object of this invention to provide such an accumulator which is reliable, maintenance free, simple in design, and easily manufactured.
This invention results from the realization that the use of a valve mechanism of prior art accumulators and the disadvantages associated therewith can be eliminated by the incorporation of a secondary piston connected to the primary piston by a secondary bellows such that the secondary piston seats on the hydraulic fluid port.
This invention features an accumulator comprising a housing including a gas chamber and a liquid chamber, a primary piston moveable in the housing and connected to the housing by a primary bellows sealing the gas chamber with respect to the liquid chamber; and a secondary piston moveable with respect to the primary piston and connected to the primary piston by a secondary bellows sealing the secondary piston with respect to the liquid chamber.
Typically there is a flow port in communication with the liquid chamber, the flow port sealable by the secondary piston. In one embodiment, the flow port is integral with the housing. In another embodiment, the flow port includes a port fitting removable from the housing.
The accumulator of this invention features a housing including a gas chamber and a liquid chamber; a primary piston moveable in the housing and connected to the housing by a primary sealing mechanism which seals the gas chamber with respect to the liquid chamber; and a secondary piston moveable with respect to the primary piston and connected to the primary piston by a secondary mechanism which seals the secondary piston.
In the preferred embodiment, the primary sealing mechanism is a primary bellows and the secondary sealing mechanism is a secondary bellows.
One accumulator of this invention includes a housing including a gas chamber and a liquid chamber; a separator between the gas chamber and the liquid chamber; and a device movable with respect to the separator and connected to the separator by a bellows seal which seals the moveable member with respect to the separator. Typically, the separator includes a primary piston movable in the housing and connected to the housing by a primary bellows sealing the gas chamber with respect to the liquid chamber. In one embodiment, the moveable member is a secondary piston moveable with respect to the primary piston and connected to the primary piston by a secondary bellows.